OK. So this file (others too?) are appended as new/different devices are plugged in.
Here is current contents of 70-persistent-cd.rules:
# This file was automatically generated by the /lib/udev/write_cd_rules
# program, probably run by the cd-aliases-generator.rules rules file.
#
# You can modify it, as long as you keep each rule on a single line
# and set the $GENERATED variable.
# DVD-RAM_UJ-842 (pci-0000:00:1f.1-scsi-0:0:0:0)
ENV{ID_CDROM}=="?*", ENV{ID_PATH}=="pci-0000:00:1f.1-scsi-0:0:0:0",
SYMLINK+="cdrom", ENV{GENERATED}="1"
ENV{ID_CDROM}=="?*", ENV{ID_PATH}=="pci-0000:00:1f.1-scsi-0:0:0:0",
SYMLINK+="cdrw", ENV{GENERATED}="1"
ENV{ID_CDROM}=="?*", ENV{ID_PATH}=="pci-0000:00:1f.1-scsi-0:0:0:0",
SYMLINK+="dvd", ENV{GENERATED}="1"
ENV{ID_CDROM}=="?*", ENV{ID_PATH}=="pci-0000:00:1f.1-scsi-0:0:0:0",
SYMLINK+="dvdrw", ENV{GENERATED}="1"
# IBM_USB_CD-ROM_Drive (pci-0000:00:1d.7-usb-0:6.3:1.0-scsi-0:0:0:0)
ENV{ID_CDROM}=="?*",
ENV{ID_SERIAL}=="TEAC_IBM_USB_CD-ROM_Drive_0000000005300129", SYMLINK+="cdrom1",
ENV{GENERATED}="1"
# IBM_USB_CD-ROM_Drive (pci-0000:00:1d.7-usb-0:6.3:1.0-scsi-0:0:0:0)
ENV{ID_CDROM}=="?*",
ENV{ID_PATH}=="pci-0000:00:1d.7-usb-0:6.3:1.0-scsi-0:0:0:0", SYMLINK+="cdrom2",
ENV{GENERATED}="1"
This is a Thinkpad X60. I have 2 'docks', one at home, one at work, each with a
different CD/DVD drive (one is a DVD-ROM, the other a DVD-RW).
This message was produced when I hot-plugged in a portable USB CD-ROM (an old,
USB1 device).
Seems a bit funny to be adding this to 'persistent' list, but I presume its
description would need to be added somewhere...

Harald, I know it is intended, I am questioning why? And why in /etc? /etc
should usually be considered a read/only directory, And things that change
should be in /var. /var/lib. /var/run, /var/cache. I can write SELinux rules
to allow the cd rules to be written for this file and protect the others. But
if this is really not a configuration file then it should be moved to another
directory. SELinux likes to be able to write to entire directories instead of
certain files in a directory.